Options can be used to synthesize a long or short position in an underlying asset.
For example, simultaneously purchasing a call and selling a put with the same strike price and same expiration has the effect of being long the stock. Gains in the stock result in the call rising in price and the put falling in price, both positions gain in value as the stock rises.
A short position in a stock can be synthesized by purchasing a put and selling a call with the same strike and expiration.
Characteristics of a synthetic position:
A trader entering a synthetic position should maintain enough capital to purchase, or hold short, the equivalent number of shares of the underlying asset in order to avoid a margin call.